Material for absorption and attenuation of neutrons

ABSTRACT

Masses for obtaining poured concrete, concrete for bricks, concrete for tiles or mortar are known, in which Portland cement and Colemanite, water and additives to regulate the process are involved as aggregate. 
     The invention achieves a remarkable increase in the capacity of neutron radiation protection of the material. For this, Portland cement is replaced by Alumina cement and a new component is inserted into the mass, specifically anhydrous calcium sulfate, the Colemanite staying as aggregate.

OBJECT OF THE INVENTION

The present invention relates to a mass, specially designed for the manufacture of high-capacity of neutron radiation protection products, such as concrete, bricks, tiles and mortars.

The object of the invention is to achieve a mass with high homogeneity, with an optimum barrier effect against neutrons of diverse energy, allowing a marked reduction of the thickness of shielding barriers against standard materials to achieve the same barrier effect to said radiation.

It is also the object of the invention to cause and/or accentuate the effect of neutron absorption in their various energies from this material, and to eliminate or significantly reduce the effect of neutron scattering indoors, which in the case of the cancer treatment bunkers, would mean that the patient would only receive the neutrons received directly from the main beam eliminating those received by the scatter effect. The electronics and room control systems are also benefited by this fact, as well as a significant reduction in the shielding of the bunker door, among other beneficial aspects.

The invention is applicable to any system of radiological protection, such as containers and/or mobile barriers of radioactive facilities, radiotherapy bunkers, or any facility where the existence of neutrons is expected.

BACKGROUND OF THE INVENTION

Concrete with capacity of radiation protection have, in addition to the usual cement components, water and chemical additives which vary according to the characteristics intended for them, such as resistance, setting time, protection against freezing, assurance of the absence of cracking, marine environment, etc., and an aggregate that distinguishes them from conventional concrete.

The problem posed by this type of concrete is that in order to provide good radiation protection properties, it is necessary to have a considerable wall thickness, with the consequent and negative impact on weight, space, and cost, since the hydrogen content in the same is usually low.

Trying to avoid this problem, the Invention Patent with Application Number P 200900481 and publication number ES 2 344 290 is known, which describes a mass for the manufacture of products with high capacity of neutron radiation protection, mass that the same as any conventional concrete, is structured based on cement, aggregates, water and chemical additives that change the characteristics of the concrete, with the particularity that said mass uses as aggregate Colemanite with a very continuous grain size to achieve a perfect homogeneity in mass, determinant of a barrier effect against neutron radiation, which allows to significantly reduce the wall thickness without diminishing the barrier effect.

More specifically, said Patent envisaged the use of Portland cement, water, Colemanite and additives.

The applicant of this Patent has discovered that the results obtained with the same can be clearly improved through the use of new components in the mass in question.

DESCRIPTION OF THE INVENTION

According to one of the features of the invention, in the mass advocated participates, rather than the aforementioned Portland cement, Alumina cement (Al₂O₃). The Alumina content of the cement is comprised between 36% and 45%, and it can reach 70%, depending on the availability of this type of product, and controlling the capacity of reaction with calcium sulfate.

According to another of the features of the invention, a new component is introduced into the mass, particularly anhydrous calcium sulfate (CaSO₄). This sulfate must have a high degree of purity.

The use of aggregate of Colemanite is maintained (Ca₂B₆O₁₁ 5H₂O), which as it is known is a calcium borate, and also the chemical additives needed for a proper production and installation or casting are maintained.

The new material, i.e. the new composition of the mass, with a volumetric distribution is as follows:

-   -   Alumina cement between 4 and 5%.     -   Water between 17 and 18%.     -   Anhydrous calcium sulfate between 5 and 5.5%.     -   Colemanite between 72 and 73.5%.     -   Additives of the order of 0.02%.

From the suitable combination between the cement with high content of Alumina and the anhydrous calcium sulfate, a quick crystallization of Ettringite (3CaO Al₂O₃ 3CaSo₄ 32H₂O) is achieved, therefore significantly increasing the number of hydrogen molecules, very effective for neutron capture primarily the fast neutrons, absorbing them or thermalizing them, these thermal neutrons being the ones that are captured by the boron contained in the mixture.

DESCRIPTION OF DRAWINGS

In order to complement the description that is being made and with the object of helping to a better understanding of the features of the invention, according to a preferred example of practical embodiment of the same, is accompanied as an integral part of the description, a set of drawings where with illustrative character and without limitation, the following has been represented:

FIG. 1—It shows a graph wherein the fluence of the neutrons in the isocenter of a bunker with simple labyrinth has been shown, wherein the walls of the same have been lined with the mass object of the invention, with a thickness of 5 cm.

FIG. 2—It shows a plot similar to FIG. 1, but in the center of the corridor of the labyrinth.

EXAMPLE OF PREFERRED EMBODIMENT OF THE INVENTION

In a practical embodiment of the mass or spilled material, the following mixture expressed in volume has been carried out:

-   -   Alumina cement . . . 4.5%     -   Water . . . 17.5%     -   Anhydrous calcium sulfate . . . 5.23%     -   Colemanite . . . 72.75%     -   Additives . . . 0.02%

These figures may vary from the order of 10% both in positive and negative sense, based on production processes to be used, curing, fraction of the aggregate to be used, and objectives of priority weight such as radiation protection coefficients, mechanical strength of the mass, cracking, etc.

In cases where the granulometric fraction of Colemanite is small in size, specifically when the maximum size of the aggregate in the fraction is less than 8 or 10 mm, variations in the dosing of the previous formulation may be even greater than 10%, due to the solubility of Colemanite in water.

Density is not a parameter pursued in a specific way, and will be the result of the optimization of the mixture. However it will be around 2.1 Kg/dm³.

As previously mentioned, the heavy mass that the invention proposes allows obtaining poured concrete, concrete for bricks, concrete for tiles or dry mortar.

The results obtained with the invention are clearly reflected in the graphs shown in FIGS. 1 and 2. 

1. Material for absorption and attenuation of neutrons, of the type including Colemanite as aggregate and cement as a binder, characterized in that the cement that participates in the same is cement with high content of Alumina, and in that it also includes anhydrous calcium sulfate, all together with the water and the additives necessary for preparing the mass.
 2. Material for absorption and attenuation of neutrons, according to claim 1, characterized in that the content of Alumina (Al₂O₃) in the cement is comprised between 36% and 70%.
 3. Material for absorption and attenuation of neutrons, according to claim 1, characterized in that the different components of the same participate with the following proportions by volume: Alumina cement . . . 4.5% Water . . . 17.5% Anhydrous calcium sulfate . . . 5.23% Colemanite . . . 72.75% Additives . . . 0.02% These amounts can vary both in positive and negative sense up to 10%.
 4. Material for absorption and attenuation of neutrons, according to claim 2, characterized in that the different components of the same participate with the following proportions by volume: Alumina cement . . . 4.5% Water . . . 17.5% Anhydrous calcium sulfate . . . 5.23% Colemanite . . . 72.75% Additives . . . 0.02% These amounts can vary both in positive and negative sense up to 10%. 